Internal network interface cards (NICs) can be either built-in to the system motherboard, as is the case with laptops/notebooks, servers and most modern motherboards, or plugged into an expansion slot inside the device. Modern NIC cards, like that shown in the image, use the PCI bus to interconnect with the system and are very easy to install. They are also available with USB and Firewire interfaces.

They provide the connectivity for not just ethernet networks, but also WI-FI and token-ring networks. NICs can also be used to connect two PCs in a peer-to-peer configuration through the use of a patch cable, which is useful for fast data transfer between the two machines.

Apart from the interface they use to interconnect with the system, NICs are advertised with a specification that refers to its data transfer rate. This figure is specified in Mbps (Megabits per second) or Gbps (Gigabits per second). Most modern network interface cards support up to 100Mbps, while some of the more expensive Gigabit ethernet cards support up to 16000Mbps (160 Gbps).

A typical NIC features an 8P8C socket which is used to connect it to the network via an RJ-45 plug, and also an LED (sometimes 2) which lights up when the card is connected and flashes during data transfer. Some older network cards may also have a BNC connector, which was used to connect to the now outdated 10BASE2 networks.

A wireless network interface controller (WNIC) is used to connect wirelessly to the network, usually by connecting to a wireless router. These NICs feature an antenna (sometimes enclosed in the casing) which has a limited range and typically come with either a PCI or USB interface. Most laptops, smartphones, tablets and other Internet-enabled devices now come with an integrated WNIC.